1. Field of the Invention
The present invention relates to a laser scanning device and an image forming apparatus, and more particularly to a laser scanning device for forming an electrostatic latent image on a photosensitive member in an image forming apparatus such as a copying machine, a printer, a facsimile or the like, and an image forming apparatus provided with the laser scanning device.
2. Description of Related Art
A laser scanning device installed in an image forming apparatus such as a copying machine, a printer, a facsimile or the like has a light source unit comprising a light emitting element (a laser diode), a collimator lens and a cylindrical lens.
JP2002-244062A discloses that a light source unit has a light emitting element and a collimator lens which are fixed to a holder, the light emitting element being press-fitted and the collimator lens being bonded. The collimator lens is positioned against the holder such that the center of the lens matches with the point of light emission and positioned in the direction of optical axis, and thereafter, the collimator lens is fixed to the holder. JP9-218368A discloses that a holder which holds a light emitting element is partly extended in the direction of optical axis and that a collimator lens, an aperture stop and a cylindrical lens are coaxially bonded and fixed to the extended portion of the holder. JP5-136952A and JP5-273483A disclose that an intermediate holder is provided between a radiator holding a light emitting element and a lens holder, that the radiator and the intermediate holder are bonded and fixed together and that the intermediate holder and the lens holder are bonded and fixed together.
According to JP2002-244062A and JP9-218368A, however, since the light emitting element is press-fitted to the holder, it is difficult to adjust the position of the light emitting element in the direction of optical axis. Therefore, the relative positions of the light emitting element and an optical element such as a collimator lens in the direction of optical axis are adjusted by moving the optical element. In the light source unit according to JP2002-244062A, the relative positions of the collimator lens and the holder are adjustable in three directions, namely, the directions for matching of the center of the lens to the point of light emission and the direction of optical axis, and the light source unit is constructed as a unit for emitting a parallel bundle of rays. However, the light source unit does not have a radiator, and there is possibility that the wavelength of light emitted from the light emitting element may change due to an increase in temperature of the light emitting element. In order to avoid this trouble, it is necessary to provide a radiator separately, which increases the number of components and the manufacturing cost. In the structure according to JP9-218368β, the lower ends of the optical elements (the collimator lens and the cylindrical lens) are fixed. Accordingly, the optical elements are adjustable only in the direction of optical axis, and it is difficult to adjust the positions of the optical elements in the vertical direction (sub-scanning direction).
In the light source unit according to JP5-136952A and JP5-273483β, because the intermediate holder is provided between the radiator holding a light emitting element and the lens holder, and the number of components is large. Since the radiator is close fixed to the intermediate holder, the radiator cannot fully perform heat radiation. Also, because there is no space between the radiator and the intermediate holder, light cannot enter between the radiator and the intermediate holder, and it is impossible to use photosetting adhesive to bond the radiator to the intermediate holder. Thus, it takes a long time to bond the radiator and the holder together, and since the bonding is unstable, high accuracy is not guaranteed.